This invention relates generally to wind turbines, and more particularly to methods and apparatus for efficiently reducing load in wind turbines.
Recently, wind turbines have received increased attention as an environmentally safe and relatively inexpensive alternative energy source. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted within a housing or nacelle, which is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 80 or more meters in diameter). Blades on these rotors transform wind energy into a rotational torque or force that drives one or more generators, rotationally coupled to the rotor through a gearbox. The gearbox may be used to step up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is fed into a utility grid. Some turbines utilize generators that are directly coupled to the rotor without using a gearbox.
Currently, the control strategy and safety concept shut down the wind turbine above a certain (cut out) wind speed. This strategy prevents damaging loads that might occur due to the higher turbulence in the wind. The disadvantage of this strategy is the lack of energy capture in the region above cut out wind speed. Also, a brief increase in wind speed might trigger a turbine shutdown, while the recovery to normal power production may take some time. On the same token, the occurrence of high turbulence at rated wind speeds will also increase the likelihood of triggering a turbine shutdown.